i replaced a txv on a trane a/H ordered factory valve and installed. i pressurize system to 300 psig through my high side it kept droppping so i figured hmm i have a leak, isolate liquid and suction lines they both hold ok its in my evap coil.
so i put a gage port on the liquid line entering txv pressurize to 300psig and it drops im going crazy for this leak so i put a gage port on my suction sideof the evap coil, then i realize its pissing through the valve slow. i heat the bulb a little and pops open cool. but here is where it gets me. if i pressurize through the txv inlet side it will hold 300psig and only go up to 175 max on the out bound side, so i pressurize in reverse through suction now its the opposite. evap side holds 300 and txv inlet will max out at 175psig its something about the pressure differential across the valve that makes it close up it my only thought never seen one act that way???????? any body encounter that or know of it?
When I pressure test a system, I equalize both sides through my manifold gauges to prevent stuff like this from tricking me into thinking there is a leak. It's the same for pulling a vacuum.
There are some old R12 valves that won't go above 50psi when pressurized.
i stopped pressurizing through my low side gage because to much pressure will cause it to warp out the bourdon tube inside the low side gage (analog style) i do have a set for 410 but i prefer the lower pressure gage gives smaller increments for setting pressure controls and stuff. i guess i could have left on the lo side gage until it got up around its max then removed ill start doing it that way. i must say i wasted an extra 2 hrs messing around looking for a leak.
Originally Posted by keviekev70